Increasing Nutrient Fluxes and Mixing Regime Changes in the Eastern Arctic Ocean

Abstract

Primary productivity in the Arctic Ocean is experiencing dramatic changes linked to the receding sea ice cover. The vertical transport of nutrients from deeper water layers is the limiting factor for primary production. Here, we compare coincident profiles of turbulence and nutrients from the Siberian Seas in 2007, 2008, and 2018. In all years, the water column structure in the upstream region of the Arctic Boundary Current promotes upward nutrient transport, in contrast to the regions further downstream, and there are first indications for an eastward progression of these conditions. In summer 2018, strongly enhanced vertical nitrate flux and primary production above the continental slope were observed, likely related to a remote storm. The estimated contribution of these elevated fluxes above the slope to the Pan‐Arctic vertical nitrate supply is comparable with the basin‐wide transport, and is predicted to increase with declining sea ice cover in the future.

Nutrient and Silicon Isotope Dynamics in the Laptev Sea and Implications for Nutrient Availability in the Transpolar Drift

“…In addition, Schulz et al. (2022) recently reported similarly low [DIN] at the Laptev Sea margin for 2018. Therefore, we conclude that the differences observed in [DIN] between the open ocean surveys conducted in 2015 and our surveys in 2013 and 2014 are linked to slight hydrological differences rather than sample treatment and analysis.…”

“…However, if stratification in the Laptev Sea continues to weaken (Janout et al., 2020), river‐bound DSi and other nutrients are more likely to be consumed on the shelves and thus prior to their export. This would result in strong lateral gradients of the future biological regimes between the central Arctic Ocean, the inner Laptev Sea shelf, and the continental slope region, which receives AW‐sourced nutrients with the boundary current and is projected to experience a future increase in productivity due to progressing Atlantification (i.e., the increasing influence of Atlantic waters) along with further reduction in stratification (Bluhm et al., 2020; Oziel et al., 2022; Schulz et al., 2022). The loss of sea ice will therefore only lead to stronger diatom‐dominated primary productivity in the central Arctic Ocean for a short period of time, if at all.…”

“…Thibodeau et al (2017) reported [DIN] data from samples used for nitrogen isotope analysis collected independently during the same summer expedition in 2014 that are overall identical within error with our data from the same expedition. In addition, Schulz et al (2022) recently reported similarly low [DIN] at the Laptev Sea margin for 2018. Therefore, we conclude that the differences observed in [DIN] between the open ocean surveys conducted in 2015 and our surveys in 2013 and 2014 are linked to slight hydrological differences rather than sample treatment and analysis.…”

Winter Vertical Diffusion Rates in the Arctic Ocean, Estimated From 7Be Measurements and Dissipation Rate Profiles

“…Vertical mixing can hence be a significant source of nutrients (Hsieh et al., 2021; Kadko et al., 2020; Lewis et al., 1986; Oschlies, 2002; Schulz, Lincoln, et al., 2022), and upward turbulent transport of nutrients is required to drive at least part of new primary production (Ledwell et al., 2008; Painter et al., 2014; Wagener et al., 2008). Primary production is therefore limited by nutrient supply mediated by physical transport mechanisms (Tremblay et al., 2015), of which vertical mixing is a key process that will determine the fate of marine Arctic ecosystems (Ardyna et al., 2014; Babin, 2020; Schulz, Lincoln, et al., 2022). However, the steep vertical density gradients in the upper Arctic Ocean hinder vertical diffusion of nutrients, such that nitrate fluxes are on average one to two orders of magnitude smaller than those observed elsewhere in the world ocean (Randelhoff et al., 2020).…”

“…However, the steep vertical density gradients in the upper Arctic Ocean hinder vertical diffusion of nutrients, such that nitrate fluxes are on average one to two orders of magnitude smaller than those observed elsewhere in the world ocean (Randelhoff et al., 2020). A quantitative assessment of vertical diffusivity in the upper ocean is hence crucial for understanding the transport of heat and nutrients in the Arctic, especially in light of the substantial changes which are anticipated for the oceanic mixing regime (Dosser et al., 2021; Polyakov et al., 2017; Schulz, Büttner, et al., 2021; Schulz, Lincoln, et al., 2022; Timmermans & Marshall, 2020).…”